1. Field of the Invention
The present invention relates to image display apparatuses, signal processing apparatuses, image display methods, and computer program products. More specifically, the present invention relates to an image display apparatus, a signal processing apparatus, an image display method, and a computer program product with which, in an arrangement where blanking-period data is displayed, degradation of blanking-period data in executing interlaced-to-progressive (IP) conversion of interlaced signals into progressive signals is prevented to achieve accurate data display.
2. Description of the Related Art
As opposed to CRT displays, which employ dot-sequential impulse driving, flat panel displays (FPDs) implemented by liquid crystal displays (LCDs) or organic electroluminescence (EL) displays employ frame-holding display methods. For example, with a typical frame frequency of 60 Hz, a flat panel display holds the same image during each frame display period ( 1/60 sec=16.7 msec) over the entire display screen.
Most content or broadcasting signals for displaying images are generated in the form of interlaced image data compatible with CRT displays. More specifically, in interlaced image content, each image displayed on the horizontal scanning lines of a CRT display is formed of two fields. First, every other horizontal scanning line is scanned from top to bottom in the first field, and then, every other horizontal scanning line that has not been scanned is scanned from top to bottom in the second field, whereby an image of one frame is displayed.
When such interlaced image content is displayed on a display apparatus that employs a frame-holding display method, such as an LCD, lines carrying display image signals and lines not carrying display image signals occur alternately in each display frame, so that flicker becomes apparent and luminance is reduced to half. In order to solve this problem, interlaced signals are converted into progressive signals, i.e., IP conversion is executed.
As opposed to interlaced scanning, in which every other horizontal scanning line is scanned from the top of the screen, progressive scanning sequentially scans a plurality of horizontal scanning lines (horizontal display lines) forming the screen. The progressive scanning provides image signals of all the lines.
When IP conversion is executed to convert interlaced signals into progressive signals, signals of lines not carrying signals included in the interlaced signals are generated by interpolation. The interlaced signals are converted into progressive signals using the pseudo-signals generated by interpolation, whereby an image corresponding to the progressive signals having signals for all the pixels is displayed. IP conversion is described, for example, in Japanese Unexamined Patent Application Publication No. 8-221039.
However, when IP conversion is executed to convert interlaced signals into progressive signals, signals of horizontal and vertical blanking periods included in original interlaced signals, i.e., signals of horizontal blanking periods for switching between horizontal lines of video signals and signals of vertical blanking periods for switching between fields, are degraded. That is, signal processing such as interpolation is also executed on the blanking-period signals as well as the video signals, causing degradation of the signals.
In blanking periods, auxiliary signals, for example, audio data, or metadata such as content property information, are recorded. Ordinary users do not usually display and check signals of the blanking periods. However, content creators or editors have a demand for displaying the signals of the blanking periods together with video content on a monitor for professional use to check for the presence of the blanking-period signals.
That is, with a monitor for professional use, there exists a demand for checking for the presence of auxiliary signals superposed in horizontal and vertical blanking periods of interlaced signals, such as audio information or metadata. In cathode-ray tube (CRT) monitors that have hitherto been available, it is possible to display blanking-period signals simply by changing display timing or position, for example, by under-scan or horizontal or vertical delay, so that special processing is not needed to display auxiliary signals.
However, in the case of a frame-holding (fixed pixel) monitor, as described earlier, when input signals are interlaced signals, IP conversion is executed to convert the interlaced signals into progressive signals. When the interpolation described above is executed on blanking-period signals, the blanking-period signals are degraded, so that it becomes difficult to check the blanking-period signals on the monitor.